Method of manufacturing a semiconductor device

ABSTRACT

A MOSFET in which the gate electrode is formed of a polycrystalline silicon film, a silicon nitride film having a nitrogen surface density of lens than 8×10 14  cm -2 , and a tungsten film--these films formed one upon another in the order mentioned. The gate electrode thus formed, serves to shorten the delay time of the MOSFET.

This is a division of application Ser No. 08/767,149 filed Dec. 16,1996, now U.S. Pat. No. 5,719,410, which is a continuation ofapplication Ser. No. 08/364,922, filed Dec. 28, 1994, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device and a method ofmanufacturing the same, and more particularly to an improvement ofelectrodes and wiring of a semiconductor device and also a method of theelectrodes and the wiring.

2. Description of the Related Art

The major sections of computers and communication apparatusesincorporate large-scale integrated circuits (LSIs), each comprising manytransistors and many resistors which are electrically connected, formingelectric circuits on a single semiconductor chip. The operatingefficiency of a computer or a communication apparatus largely depends onthe operating efficiencies of the LSIs used in the computer or theapparatus. The operating efficiency of each LSI can be enhanced byincreasing the integration density of the LSI--that is, by making theelements constituting the LSI smaller.

In recent years, the sizes of LSI elements have been reduced. Thanks tothe size-reduction of LSI elements, the integration densities of LSIshave been increased and the operating speeds thereof have been raised.The higher the speed of each LSI element, the more greatly it isrestricted by the RC delay of the gate electrode or gate wiring of theLSI element.

The RC delay can be decreased by increasing the thickness of the gateelectrode or the gate wiring, thereby decreasing the resistance of theelectrode or wiring, even if the material of the gate electrode or thegate wiring is not changed. An increase in the thickness of the gateelectrode or wiring is, however, problematical in view of the process offorming the gate electrode or the gate wiring. In the case of the gateelectrode, it is desired that its aspect ratio (i.e., the ratio of thegate height to the gate length) should not greatly exceed the value of1.

There is available a method of decreasing the resistance of the gateelectrode without increasing the thickness of the electrode. The methodis to form the electrode of a two-layer film consisting of apolycrystalline silicon layer and a refractory metal silicide layer. Ifthis method is employed, the threshold voltage of the LSI element havingthe gate electrode can be controlled by the method used in theconventional process of forming silicon gates. In addition, such atwo-layer film can be easily formed by the conventional process offorming silicon gates since most refractory metal silicides have highthermal resistance.

If a MOSFET having a gate length of, for example, 0.3 μm or less has itsgate electrode made of such a two-layer film, the thickness of therefractory metal silicide layer is limited to about 100 to 200 nm. Inthis case, the sheet resistance of the gate electrode layer can bedecreased to only about a few tens of ohms per unit area.

Assume that a gate electrode having a width of 0.25 μm and a sheetresistance of about 1Ω/□ has been formed of a two-layer film whichconsists of a polycrystalline silicon layer and a refractory metalsilicide layer. Then, the refractory metal silicide layer has athickness of about 1 μm. Inevitably, this gate electrode has an aspectratio as high as 4 to 5. It is therefore difficult to pattern the gateelectrode and to form an inter-layer insulating film on the patternedgate electrode.

It has been proposed that the small gate electrode of a MOSFET be madeof a two-layer film consisting of a layer of a polycrystalline siliconlayer and a refractory metal layer (e.g., a tungsten or molybdenumlayer) which has a lower resistance than refractory metal silicides butsufficient thermal resistance, so that the gate may have a thickness of100 nm and a sheet resistance of a few ohms per unit area. If therefractory metal layer is made of tungsten, tungsten reacts with siliconat a temperature of about 600° C., forming tungsten silicide, though itis said to hardly react with silicon. As a consequence, the resistanceof gate electrode increases.

To prevent the reaction of tungsten with silicon, a reaction-inhibitingfilm may be interposed between a polycrystalline silicon layer and arefractory metal layer. Jpn. Pat Appln. KOKAI Publication No. 60-195975,for example, discloses that a silicon nitride film effectively preventsa molybdenum layer from reacting with a polycrystalline silicon layer.The publication teaches that the silicon nitride film should desirablyhave a thickness ranging from 1 nm to 5 nm in order to allow a tunnelcurrent to flow between the molybdenum layer and the polycrystallinesilicon layer.

As the element size is reduced, it becomes more difficult to control thesize of any part of the element and to provide the part in a desiredshape. The size of the gate electrode of a MOSFET greatly affect theoperating efficiency of the MOSFET. Hence, it is demanded that processtechniques be developed for providing a gate electrode whose width (gatelength) is little different from the design size.

A two-layer film consisting of a layer of a polycrystalline siliconlayer and a tungsten layer (a refractory metal layer) may be dry-etchedto form the gate electrode of a MOSFET. If this is the case, thetwo-layer film is etched for a time long enough to etch away a filmwhich has the same structure but is a thicker by α. The process foretching a film of the extra thickness is known as "over etching." Theover etching must be performed because a two-layer film generally has atleast one portion thicker than the other portions. Unless the film isetched even after the other portions have been etched, its thickerportion cannot be etched completely.

Here arises a problem. The tungsten layer is etched more slowly than thepolycrystalline silicon layer. The polycrystalline silicon layer isgreatly etched when the tungsten layer is over-etched. Assume that thetwo-layer film is dry-etched by, for example, RIE (Reactive Ion Etching)in which SF₆ gas and Cl₂ gas are applied to the two-layer film at flowrates of 40 SCCM and 10 SCCM, respectively, in an atmosphere at apressure of 10 mTorr, a high-frequency voltage of 0.7 W/cm² is appliedto the two-layer film, and the two-layer film is maintained at 70° C.Then, the tungsten layer is etched at the rate of about 180 nm/min,whereas the polycrystalline silicon layer beneath the tungsten layer isetched at the rate of about 700 nm/min. The ratio of the etching rate ofthe tungsten layer to that of the polycrystalline silicon is inevitablyas low as about 0.3.

Hence, even of the two-layer film which consists of a layer of apolycrystalline silicon layer and a tungsten layer (a refractory metallayer) is dry-etched, it is impossible to form a patterned gateelectrode which has a desired shape.

SUMMARY OF THE INVENTION

The first object of the present invention is to provide a semiconductordevice in which the delay of signal transfer, resulting from contactresistance, is decreased, and also a method of manufacturing thesemiconductor device.

The second object of the invention is to provide a semiconductor devicewhich has electrodes (wiring), each made of a two-layer film which isnot oxidized excessively and which is comprised of a first conductivelayer containing silicon and nitrogen and a second conductive layer, andalso to provide a method of manufacturing the semiconductor device.

The third object of the invention is to provide a semiconductor devicewhich has electrodes (wiring) easy to pattern to have desired shapes,and to provide a method of manufacturing the semiconductor device.

To achieve the first object, there are provided two semiconductordevices and a methods of manufacturing either device.

According to the first aspect of the invention, there is provided asemiconductor device comprising at least one of an electrode and awiring which comprises: a silicon film; a film formed on the siliconfilm, containing nitrogen and silicon and having a nitrogen surfacedensity of less than 8×10¹⁴ cm⁻² ; and a refractory metal film formed onthe film.

According to the second aspect of the invention, there is provided asemiconductor device comprising at least one of an electrode and awiring which comprises: a silicon film; a first film formed on thesilicon film, containing nitrogen and silicon and having a nitrogensurface density of less than 8×10¹⁴ cm⁻² ; a second film formed on thefirst film, containing refractory metal and nitrogen; and a third filmformed on the second film, the third film being made of the refractorymetal.

According to the third aspect of the invention, there is provided amethod of manufacturing a semiconductor device, comprising the steps of:forming a silicon film on a substrate; forming a first film containingmetal and nitrogen on the silicon film, the metal being of such a typethat a negative value is obtained by subtracting a decrease in Gibbsfree energy occurring in forming a nitride of silicon from a decrease inGibbs free energy occurring in forming a nitride of the metal; andheating the film, thereby changing all or part of the first film to asecond film made of the metal and forming a third film containingnitrogen and silicon between the second film and the silicon film toform at least one of an electrode and a wiring which includes thesilicon film, the second film, and the third film.

In the semiconductor devices and the method, described above, it isdesirable that the metal be a refractory metal and that the filmcontaining nitrogen and silicon have a nitrogen surface density of lessthan 8×10¹⁴ cm⁻².

The refractory metal is, for example, tungsten or molybdenum. Preferableas refractory metal is one which does not chemically react with thefilm. The metal may be, for example, molybdenum, tungsten, niobium,tantalum or copper. On the film of the refractory metal which does notchemically react, there may be formed a metal film which is made mainlyof copper or silver.

The nitrogen surface density is the number of nitrogen atoms existingper unit area and can be measured by, for example, X-ray Photoelectronspectroscopy (XPS).

It does not matter even if the film containing nitrogen and siliconcontains a component of the atmosphere, such as oxygen. For instance, noproblem will arise even if the film contains 20% of oxygen. The filmcontaining nitrogen and silicon is not limited to one formed by there-distribution of nitrogen from a film containing a refractory metaland nitrogen. The film may be one formed by nitriding performed in anNH3 atmosphere or one formed by plasma-nitriding conducted in anitrogen-containing atmosphere.

To achieve the second object described above, there are provided asemiconductor device and a method of manufacturing the device.

According to the fourth aspect of the invention, there is provided amethod of manufacturing a semiconductor device, comprising the steps of:forming a semiconductor film on a substrate; forming a first conductivefilm containing refractory metal and nitrogen on the semiconductor film;and heating the first conductive film, thereby changing all or part ofthe first conductive film to a second conductive film made of refractorymetal and forming a third conductive film containing nitrogen andsemiconductor element of the semiconductor film to form at least one ofan electrode and a wiring which includes the semiconductor film, thesecond conductive film, and the third conductive film. Preferably, thefirst conductive film is an amorphous conductive film.

According to the fifth aspect of the invention, there is provided amethod of manufacturing a semiconductor device, comprising the steps of:forming a semiconductor film on a substrate; forming a first conductivefilm containing refractory metal and nitrogen on the semiconductor film;and heating the first conductive film, thereby changing all or part ofthe first conductive film to a second conductive film containingnitrogen, the refractory metal, and semiconductor element of thesemiconductor film to form at least one of an electrode and a wiringwhich includes the semiconductor film and second conductive film.

To achieve the third object described above, there are provided asemiconductor devices and a method of manufacturing the device.

According to the sixth aspect of the invention, there is provided asemiconductor device comprising at least one of an electrode and awiring, comprising: a semiconductor film; a first conductive film formedon the semiconductor film, containing carbon and semiconductor elementof the semiconductor film; and a second conductive film formed on thefirst conductive film. It is desirable that the ratio of carbon atoms inthe silicon carbide film range from 50 to 75 atomic %. Also is itpreferable that the silicon carbide film contain an electrically activeimpurity. Further, it is desirable that the silicon carbide film have athickness of at least 5 nm.

According to the seventh aspect of the invention, there is provided amethod of manufacturing a semiconductor device, comprising the steps of:forming a silicon film on a semiconductor substrate; forming a siliconcarbide film on the silicon film, the silicon carbide film having aratio of carbon atoms ranging from 50 to 75 atomic %; forming a metalfilm on the silicon carbide film; and performing selective anisotropicetching on the silicon film, the silicon carbide film and the metalfilm, thereby forming at least one of an electrode or a wiring. Thesilicon carbide film is formed, first by forming a carbon film on thesilicon film, and then by implanting ions into the carbon film, therebymixing carbon atoms and silicon atoms at an interface between the carbonfilm and the silicon film.

The inventors have found that in the case of a multi-layer electrodemade of a silicon film, a film containing nitrogen and silicon, and arefractory point metal, the delay of signal-transfer through theelectrode can be much reduced when the contact resistance RC decreasesbelow 100 Ωμm². They also found that the film containing nitrogen andsilicon needs to be less than 8×10¹⁴ cm⁻² in order to obtain a contactresistance of less than 100 Ωcm². When the first film containingrefractory metal and nitrogen and the second film of refractory metalwere used in place of a refractory metal film, the same results wereobtained as in the case of using a refractory metal film.

Based on their finding, a film containing nitrogen and silicon which hasa nitrogen surface density of less than 8×10¹⁴ cm⁻² is incorporated inthe semiconductor devices according to the invention. Due to the lownitrogen surface density, the electrode or the wiring is relatively low,and the delay time thereof is relatively short.

In the method of manufacturing a semiconductor device, according to thepresent invention, a film containing metal and nitrogen is formed on asilicon film. As described above, the metal contained in the film issuch a type that a negative value is obtained by subtracting a decreasein Gibbs free energy occurring in forming a nitride of silicon, from adecrease in Gibbs free energy occurring in forming a nitride of themetal. Therefore, when heat treatment is performed after the the film ofthe metal has been formed on the film containing the metal and nitrogen,the nitrogen will move from the film into the silicon film and diffusefrom the film towards to the metal film. As a result, the film willchange to a film of that metal, and a film containing nitrogen andsilicon will be formed between the metal film and the silicon film. Withthis method it is easy to control the surface density of nitrogen of thefilm containing nitrogen and silicon, to a desired value of less than8×10¹⁴ cm⁻². The semiconductor device of this invention can therefore bemade easily.

The results of the inventors, research show that when a three-layer filmcomprised of the silicon film, the conductive film formed on the siliconfilm and containing nitrogen and silicon and the second conducive filmformed on the first conductive film is oxidized, the first conductivefilm would not be oxidized excessively oxidized. Having the three-layerfilm, the electrode or wiring used in the semiconductor device is,therefore, free of abnormal oxidation.

Moreover, the results of the inventors' research show that if the firstconductive film is an amorphous one, the second conductive film can beone comprised of large crystal grains and, hence, having a low specificresistance. The mechanism of forming large crystal grains may beinferred as follows, though not confirmed yet.

The second conductive film has strain due to the specific crystalstructure of the first conductive film on which the second conductivefilm is formed. Hence, if the first conductive film has differentcrystal structures at different portions, the second conductive filmwill have different strains at the portions which are located on saidportions of the first conductive film. In the case where the secondconductive film has a thickness greater than a particular value, and thestrain in it increases over a certain magnitude, there will be formedgrain boundaries in the second conductive film. Large crystal grains canno longer be formed. On the other hand, if the first conductive film isamorphous, the second conductive film formed on the first will have nodifferent strains at different portions. However thick the secondconductive film is, no grain boundaries will be formed in the secondconductive film. Large crystal grains will therefore be formed, reducingthe specific resistance of the second conductive film.

In the method of manufacturing a semiconductor device, according to theinvention, all or part of said first conductive film is heated andthereby changed to the third conductive film which contains nitrogen,silicon and the refractory metal. The third conductive film, thusformed, is used as a reaction-preventing film. The speed with which thethird conductive film is formed depends, but very little, on the heatingtemperature. In addition, the thickness of the third conductive filmdepends little on the time of heating. Therefore, the third conductivefilm can have a large process margin and be processed to have such asize and a shape as designed.

As described above, the electrode or the wiring according to thisinvention is formed of a metal film, a silicon film and a siliconcarbide film interposed between said metal film and said silicon film.Silicon carbide is a substance very stable, both thermally andchemically. Any additive diffuses in a silicon carbide film at a speedabout two orders higher than in a silicon film. The silicon carbide filmcan therefore function as a reaction-preventing film. Furthermore, sincethe silicon carbide film is a semiconductor, it can make areaction-preventing film which excels in electrical conductivity. Theelectrode or wiring according to the invention can therefore be veryheat-resistant and have a low resistance. Still further, since selectiveetching can be performed on the refractory metal film, with respect tothe silicon carbide film, the electrode or wiring can have a size andshape as designed.

Additional objects and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and obtained by means ofthe instrumentalities and combinations particularly pointed out in theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate presently preferred embodiments ofthe invention, and together with the general description given above andthe detailed description of the preferred embodiments given below, serveto explain the principles of the invention.

FIGS. 1A to 1D are sectional views, explaining a method of forming agate electrode which is the first embodiment of the present invention;

FIG. 2 is a diagram representing the relationship between the thicknessof a silicon nitride film and the contact resistance of the film;

FIG. 3 is a diagram illustrating the relationship between the thicknessof a reaction-preventing film and the sheet resistance of a tungstenfilm;

FIGS. 4A and 4B are sectional views for explaining two modifications ofthe method two modifications of the gate electrode according to thefirst embodiment;

FIGS. 5A to 5C are sectional views, explaining a method of forming agate electrode which is the second embodiment of the present invention;

FIG. 6 is a sectional view of a MOSFET which is the third embodiment ofthe invention;

FIG. 7 is a sectional view showing a wiring which is the fourthembodiment of the present invention;

FIGS. 8A to 8D are sectional views, explaining a method of forming agate electrode which is the fifth embodiment of this invention;

FIG. 9 is a sectional view depicting a MOSFET which is a sixthembodiment of this invention;

FIGS. 10A to 10D are sectional views for explaining a method of forminga gate electrode which is the seventh embodiment of the presentinvention;

FIGS. 11A and 11B are a sectional view of a gate electrode and anequivalent circuit diagram thereof, respective, for explaining the RCdelay inherent in the gate electrode;

FIGS. 12A and 12B are another sectional view of a gate electrode andanother equivalent circuit diagram thereof, respective, for explainingthe RC delay inherent in the gate electrode;

FIG. 13 is a graph indicating the relationship between delay time andcontact resistance;

FIGS. 14A and 14B are sectional views of a gate electrode, forexplaining how the titanium nitride, a component of the electrode, isoxide abnormally;

FIGS. 15A to 15H are sectional views explaining a method ofmanufacturing a MOSFET which is the eighth embodiment of this invention;

FIGS. 16A to 16E are sectional views explaining a method ofmanufacturing a MOSFET which is the ninth embodiment of this invention;and

FIG. 17 is a schematic diagram illustrating a dry etching apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described, with referenceto the accompanying drawings.

First Embodiment

A method of forming a gate electrode which is the first embodiment ofthe invention, will be described with reference to FIGS. 1A to 1D.

First, as shown in FIG. 1A, a silicon oxide film 2 is formed on asilicon substrate 1. Then, a polycrystalline silicon film 3 is formed onthe silicon oxide film 2. The film 3 is 100 nm thick and contains anelectrically conductive impurity. The oxide film naturally formed on thepolycrystalline silicon film 3 is removed.

Next, as shown in FIG. 1B, a tungsten nitride film 4 (e.g., W₂ N or WNfilm) having a thickness of 10 nm is formed on the polycrystallinesilicon film 3 by means of reactive sputtering in an atmosphere whichconsists of N₂ gas and Ar gas mixed together in the ratio of 3:2. Atungsten film 5, 100 nm thick, is then formed on the tungsten nitridefilm 4 by sputtering conducted in an Ar atmosphere. The sputtering forforming the tungsten nitride film 4 and the sputtering for forming thetungsten film 5 should preferably be continuously performed in the ordermentioned, without exposing the tungsten nitride film 4 to theatmosphere. Alternatively, the films 4 and 5 may be deposited on thepolycrystalline silicon film 3 immediately after the film 3 has beenformed, so that the film 3 may not be exposed to the atmosphere and anoxide film may not be formed on the film 3.

Then, as shown in FIG. 1C, the structure shown in FIG. 1B is heated atabout 750 to 1000° C. in an inert gas atmosphere, a non-oxidizingatmosphere such as a reducing atmosphere (e.g., a nitrogen atmosphere,an argon atmosphere, a hydrogen atmosphere, or an atmosphere ofnitrogen, argon and hydrogen mixed together). A part of the nitrogen inthe tungsten nitride film 4 is distributed into the polycrystallinesilicon film 3, forming a nitrogen-rich film in the upper surface of thepolycrystalline silicon film 3. The nitrogen-rich silicon shall bereferred to as "silicon nitride (SiN_(x)) film 6" hereinafter. Thesilicon nitride film 6, thus formed, can have a thickness of 1 nm orless. In fact, silicon nitride films actually formed in this method werefound to have a thickness ranging from about 0.2 to about 1 nm, whenmeasured by X-ray Photoelectron spectroscopy.

While said part of the nitrogen in the film 4 moves into the film 3,thus forming the silicon nitride film 6, the remaining nitrogen in thefilm 4 diffuses outwards from the film 4. As a result, the tungstennitride film 4 changes to a tungsten film and subsequently becomesintegral with the tungsten film 5.

Why a part of of nitrogen moves from the tungsten nitride film 4 intothe polycrystalline silicon film 3 will be explained. Gibbs free energydecreases when tungsten nitride is formed from tungsten. This decreasein Gibbs free energy is less than the decrease in Gibbs free energywhich accompanies the forming of silicon nitride from silicon. Itfollows that as long as the tungsten nitride film 4 contacts thepolycrystalline silicon film 3, nitrogen in the film 4 has a chemicalpotential higher than that of the polycrystalline silicon film 3. Hence,nitrogen moves from the tungsten nitride film 4 into the polycrystallinesilicon film 3.

As described above, the remaining nitrogen in the film 4 diffuses out ofthe film 4. This is because Gibbs free energy, which has beendecreasing, starts increasing, whereby the nitrogen diffuse outwards toachieve thermodynamic equilibrium.

If a native oxide film has been formed on the surface of thepolycrystalline silicon 3, the tungsten nitride film 4 and the tungstenfilm 5 may be deposited on this oxide film, and the resultant structuremay be heat-treated in the manner described above. Then, a siliconnitride (SiO_(x) N_(y)) film containing oxygen diffused from the nativeoxide film will be formed instead of the silicon nitride (SiN_(x)) film6.

Finally, as shown in FIG. 1D, the tungsten film 5, the silicon nitridefilm 6 and the polycrystalline silicon film 3 are patterned by etching.A gate electrode is thereby provided.

FIG. 13 is a graph indicating the relationship between delay time andcontact resistance, which the inventors of this invention have foundbased on their experiments. As evident from FIG. 13, the delay timesharply changes at the contact resistance of 100 Ωcm². The delay ofsignal transfer through the gate electrode can be greatly reduced bydecreasing the contact resistance to a value less than 100 Ωcm².

The contact resistance of the silicon nitride film 6 and the thicknessthereof have the relationship shown in FIG. 2. In FIG. 2, the curve aindicates how the contact resistance changes with the thickness of thefilm 6 in the case where the polycrystalline silicon film 3 has a highn-type impurity concentration. On the other hand, the curve b shows howthe contact resistance changes with the thickness of the film 6 in thecase where the film 3 has a high p-type impurity concentration.

FIG. 2 teaches two things. First, in the case where the polycrystallinesilicon film 3 has a high p-type impurity concentration, the surfacedensity of nitrogen at the interface between the tungsten film 5 and thesilicon nitride film 6 needs to be less than 8×10¹⁴ cm⁻² (equivalent toless than 1 nm in terms of the thickness of the film 6) in order toobtain a contact resistance of less than 100 Ωcm². Secondly, the contactresistance of the film 6 greatly changes at the nitrogen surface densityof 8×10¹⁴ cm⁻² and can be much reduced by setting the that density at avalue less than 8×10¹⁴ cm⁻².

As described above, the method of forming a gate electrode according tothe invention can set the surface density of nitrogen at the interfacebetween the films 5 and 6 at a value less than 8×10¹⁴ cm⁻². Therefore,the silicon nitride film 6 can be made thin enough to reduce have itscontact resistance reduced, whereby the delay of signal transfer throughthe gate electrode can be decreased.

FIG. 3 is a graph illustrating the relationship which the nitrogeninterface density of a gate electrode consisting of a polycrystallinesilicon film, a reaction-preventing film and a tungsten film has withthe sheet resistance the tungsten film having a thickness of 100 nmexhibits after the gate electrode has been heated in an N₂ atmosphere at800° C. for one hour. More precisely, FIG. 3 shows the relationshipbetween the nitrogen interface density of a gate electrode consisting ofa polycrystalline silicon film, a reaction-preventing film of SiN_(x) orSiO_(x) N_(y) and a tungsten film and the sheet resistance of thetungsten film, and also indicates the relationship between the thicknessof the reaction-preventing film of SiN_(x) or SiO_(x) N_(y) and atungsten film and the sheet resistance of the tungsten film.

As can be understood from FIG. 3, if the reaction-preventing film ismade of SiN_(x) or SiO_(x) N_(y) as in the first embodiment of theinvention, the sheet resistance of the tungsten film remainssufficiently low (equivalent to 0.3 nm in terms of the thickness of theSiN_(x) film) at a nitrogen interface density of 2.2×10¹⁴ cm⁻² andupwards. Hence, the silicon nitride film 6 (i.e., thereaction-preventing film) greatly mitigates the influence of the heattreatment.

In contrast, if the reaction-preventing film is made of SiO₂ as in theconventional process of forming silicon gates and has a thickness of 2nm or less, the sheet resistance of the tungsten film will increase asevident from FIG. 3. This is because the tungsten film and thepolycrystalline silicon film react with each other, inevitably formingsilicide.

In the method of forming a gate electrode according to the invention,the polycrystalline silicon film 2 may be slightly nitrided, forming avery thin silicon nitride film--due to the plasma generated in theprocess atmosphere as the tungsten nitride film 4 is formed bysputtering. This silicon nitride film can be used as areaction-preventing film, in addition to the silicon nitride film whichhas been formed by the nitrogen distribution from the tungsten nitridefilm 4.

In the method of forming the gate electrode which is the firstembodiment, the tungsten nitride film 4 is changed, as a whole, into atungsten film. Alternatively, as shown in FIG. 4A, only a portion of thetungsten nitride film 4 may be changed into a tungsten film. In thiscase, the thickness of that portion of the film 4 depends on thethickness of the silicon nitride film 6 required.

Furthermore, as shown in FIG. 4B, a relatively thick tungsten nitridefilm 4a may be formed on the polycrystalline silicon film 3, thereby toobtain the structure illustrated in FIG. 1C. More specifically, afterthe step explained with reference to FIG. 1A, a tungsten nitride film 4aabout 100 nm thick is formed on the polycrystalline silicon film 3 bysputtering in an atmosphere containing nitrogen, excited nitrogen orionized nitrogen. Next, the resultant structure is heat-treated in anon-oxidizing atmosphere such as a reducing atmosphere, as in the methodof forming the first embodiment. The nitrogen therefore moves from thetungsten nitride film 4a into the polycrystalline silicon film 3,forming a silicon nitride film which has a thickness of about 1 nm,i.e., about one-atom layer thickness. At the same time, the nitrogendiffuses outwards from the film 4a, whereby the tungsten nitride film 4abecomes a tungsten film. As a result, the structure of FIG. 1C isobtained.

In the first embodiment, the films 3, 5 and 6 of the structure shown inFIG. 1C are patterned into a gate electrode after the nitrogen has beendistributed into the polycrystalline silicon film 3 and diffusedoutwards from the tungsten nitride film 3. If the patterning is effectedby anisotropic etching, the ratio of etching rate of the tungsten film 5to that of the polycrystalline silicon film 3 may change as the tungstengrains grow as the heat treatment proceeds. To avoid such changes in theratio of etching rates, it suffices to perform the patterning first andthen the heat treatment to distribute and diffuse the nitrogen from thetungsten nitride film 4. This heat treatment for forming the tungstennitride film 4 may be replaced by other heat treatment to be performedlater, for example, the heat treatment for activating the impurity in asource diffusion layer or a drain diffusion layer.

Second Embodiment

A method of forming a gate electrode which is the second embodiment ofthe invention, will be described with reference to FIGS. 5A, 5B and 5C.

First, as shown in FIG. 5A, a silicon oxide film 12 is formed on asilicon substrate 11. Then, a polycrystalline silicon film 13 having athickness of 100 nm is formed on the silicon oxide film 12.

Next, as shown in FIG. 5B, a silicon nitride film 14 having a smallthickness of less than 1 nm, preferably about 0.7 nm, is formed as areaction-preventing film on the polycrystalline silicon film 13. It isdesirable that the thin silicon nitride film 14 be formed by one of thefollowing five alternative methods:

(1) Thermal nitriding performed in an NH3 atmosphere at 1000° C. for 30seconds

(2) Plasma nitriding conducted in an atmosphere containing nitrogen

(3) Thermal CVD effected at 600 to 800° C., using SiH₂ Cl₂ +NH₂ or SiH₄+NH₃ as source gas

(4) Plasma CVD method

(5) Method wherein plasma (N2/N2 or NH3) is generated remote from thesubstrate heated at from 500 to 800° C., and active species of plasmaare carried to the substrate in a down flow

Thereafter, a tungsten film 15, 100 nm thick, is formed on the siliconnitride film 14 by means of sputtering.

Finally, as shown in FIG. 5C, the tungsten film 15, the silicon nitridefilm 14 and the polycrystalline silicon film 13 are patterned byetching. A gate electrode is thereby provided.

The gate electrode thus formed is as thin as that one provided by themethod according to the first embodiment, and can therefore achieve thesame advantages as the gate electrode according to the first embodiment.

Both the first embodiment and the second embodiment are gate electrodes.Nonetheless, the present invention can be applied to any other type ofan electrode and a wiring.

Third Embodiment

FIG. 6 is a sectional view of a MOSFET which is the third embodiment ofthe present invention. The method of manufacturing this MOSFET will bedescribed.

First, an insulating film 22 is formed in the surface of a siliconsubstrate 21, for isolating elements which will be formed later. A gateoxide film 23 is then formed on the exposed surface of the siliconsubstrate 21. Further, a polycrystalline silicon film 24 is formed onthe gate oxide film 23, a silicon nitride film 25 is formed on the film24, and a tungsten film 26 is formed on the film 25. The films 24, 25and 26 constitute a three-layer film. The silicon nitride film 25 isthin enough to have as low a contact resistance as possible, in order todecrease the delay of signal transfer through the MOSFET as much aspossible.

Next, a silicon nitride (SiN) film 27 is formed on the tungsten film 26.This silicon nitride film 27 serves as a cap-insulating film. Thesilicon nitride film 27 is formed by LPCVD method in a process chamber,using as source gases NH₃ gas and inorganic silane-based gas SiH₂ Cl₂,as usual. If NH₃ and SiH₂ Cl₂ are introduced together into the processchamber, the surface of the tungsten film 26 will be nitrided notuniformly, and silicon nitride will grow in the form of granules, andthe film 27 may fail to function as a cap-insulating film. To avoid thisconsequence it is advisable to introduce only SiH₂ Cl₂ into the chamber,thereby to form a thin, silicon-containing film on the tungsten film 26,and then to introduce both NH₃ and SiH₂ Cl₂ are into the processchamber. When this two-stage gas introduction was performed, the surfaceof a tungsten film was nitrided uniformly, successfully forming ahomogeneous silicon nitride film which corresponds to the film 27.

Then, the three-layer film comprised of the polycrystalline silicon film24, the silicon nitride film 25 and the tungsten film 26 is patterned byetching, thereby forming a gate electrode. N₂ gas and an H₂ --H₂ Omixture gas are applied to the resultant structure, oxidizing only thepolycrystalline silicon layer 24 and the silicon substrate 21. The oxidefilm on the gate electrode therefore becomes thick at the end portionsof the gate electrode. This makes the gate electrode work reliably evenif electric fields are concentratedly applied to the ends of the gateelectrode.

Next, an impurity is ion-implanted into the substrate 21, thus formingtwo low impurity-concentration diffusion layers 28 (i.e., a source-drainregion). A silicon nitride film 29 is then formed, which serves as aninsulating film covering the sides of the gate electrode. The film 29may be formed in the same way as the silicon nitride film 27 which isused as a cap-insulating film.

The silicon nitride films 27 and 29 completely cover the gate electrodeconstituted of the polycrystalline silicon film 24, the silicon nitridefilm 25 and the tungsten film 26. Therefore, the tungsten film 26 isfree from oxidation in the oxidation which will be subsequentlyconducted in an oxidizing atmosphere. Further, when a wiring made ofelectrically conductive material including copper (Cu) is formed thestructure of FIG. 6, the silicon nitride films 27 and 29 prevent thecopper from diffusing into the gate electrode. Still further, since thefilms 27 and 29 cooperate to wrap, as it were, the films 24, 25 and 26together, the polycrystalline silicon film 24 and the silicon nitridefilm 25 are firmly bonded to each other.

Finally, a diffusion layer 30 having a high impurity concentration isformed in the surface of the silicon substrate 21, and a metal silicidefilm 31 is formed on the diffusion layer 30. Thus manufactured is theMOSFET of the structure illustrated in FIG. 6.

Fourth Embodiment

FIG. 7 is a sectional view showing a wiring which is the fourthembodiment of the invention. With reference to FIG. 7 it will beexplained how the wiring is formed.

At first, an insulating film 42 for isolating elements and an impuritydiffusion layer 43 are formed in the surface of a silicon substrate 41.Then, an SiO₂ film 44 is formed on the entire upper surface of theresultant structure. The SiO₂ film 44 is about 600 nm thick andfunctions as an inter-layer insulating film. A contact hole 45 is madein the SiO₂ film 44, thereby exposing the impurity diffusion layer 43.Next, a polycrystalline silicon film 46, about 100 nm thick, is formedin the contact hole 45 and on the SiO₂ film 44. Further, a thin siliconnitride film 47 is formed on the polycrystalline silicon film 46, and atungsten film 48 having a thickness of about 100 nm is formed on thesilicon nitride film 47. The films 46, 47and 48 constitute a three-layerfilm, which may be formed by any method described above. Finally, thethree-layer film thus formed is patterned by etching, thereby formingthe wiring shown in FIG. 7.

Made relatively think, the silicon nitride film 47 has a low contactresistance. The delay of signal transfer through the wiring is thereforeshort.

Fifth Embodiment

FIGS. 8A to 8D are sectional views which explain a method of forming agate electrode which is the fifth embodiment of this invention. withreference to FIGS. 8A to 8D it will be described how this gate electrodeis formed.

First, as shown in FIG. 8A, a silicon oxide film 52 used as agate-insulating film is formed on a silicon substrate 51. Apolycrystalline silicon film 53 having a thickness ranging from 1 nm to10 nm is formed on the silicon oxide film 52.

Next, as shown in FIG. 8B, a tungsten nitride film 54, about 1 to 10 nmthick, is formed on the polycrystalline silicon film 53. A tungsten film55, 10 nm thick, is formed on the tungsten nitride film 54. To statemore specifically, reactive sputtering is carried out, using a tungstentarget in an atmosphere, thereby forming the tungsten nitride film 54 onthe film 53. Thereafter, N₂ gas is expelled from the process chamberused, and sputtering is then performed in the chamber now containing Ar.The tungsten film 55 is thereby formed in a vacuum, without exposing thetungsten nitride film 54 to the atmosphere.

Alternatively, both the tungsten nitride film 54 and the tungsten film55 can be formed by means of CVD method. If this is the case, thetungsten nitride film 54 is formed at 500 to 700° C., using a mixturegas, WF₆ +NF₃, as source gas, and the tungsten film 55 is formed at 400to 500° C., using a mixture gas, WF₆ +H₂, as source gas.

Thereafter, as shown in FIG. 8C, the resultant structure is subjected toheat treatment for 30 minutes at 800° C. or more in a reducingatmosphere containing hydrogen. The tungsten nitride film 54 is therebychanged into a reaction-preventing film 56 which consists of tungsten(W), silicon (Si) and nitrogen (N) (W:Si:N=1:3:1-1:4:1, for example) andwhich has a thickness of 1 nm or less. Since the heat treatment iseffected in a reducing atmosphere, the tungsten film 55 remains free ofoxidation.

How the reaction-preventing film 56 is formed will be explained. Duringthe heat treatment, part of the nitrogen in the tungsten nitride film 54leaks outside through the tungsten film 55 and diffuses into thepolycrystalline silicon film 53, forming a tungsten film, which becomesintegral with the tungsten film 55. Meanwhile, part of the tungstennitride film 54 diffuses into the polycrystalline silicon film 53,whereas part of the polycrystalline silicon film 54 diffuses into thetungsten nitride film 54. As a result, the reaction-preventing film 56is formed, which consists of tungsten, silicon and nitrogen.

The reaction-preventing film 56 may contain the oxygen derived from theoxide film naturally formed on the polycrystalline silicon film 53. Evenif this happens, the barrier at the interface between thepolycrystalline silicon film 53 and the tungsten film 55 remain intact.

The reaction-preventing film 56 can easily be formed as designed, forreasons stated above in Summary of the Invention. Being electricallyconductive, the film 56 has but a low contact resistance with thepolycrystalline silicon film 53, and also with the tungsten film 55.When put to cross-section TEM observation and EDX analysis, the film 56was found to made up of 20% of tungsten, 60% of silicon, and 20% ofnitrogen.

At last, as shown in FIG. 8D, the three-layer film formed of thepolycrystalline silicon film 53, the reaction-preventing film 56 and thetungsten film 55 is patterned into a gate electrode.

The polycrystalline silicon film 53 has a thickness of, in most cases,0.5 to 0.2 μm. An impurity, either n⁺ (As,P) or p⁺ (B), is introducedinto the polycrystalline silicon film 53 by means of ion implantation orvapor-phase diffusion, while the film 53 is being vapor-deposited orafter the film 53 has been vapor-deposited. In order to impart differentwork functions to the gates the p-channel and n-channel transistorsconstituting the CMOS-FET, B may be introduced into the gate of thep-channel transistor, and P or As may be introduced into the gate of then-channel transistor. Alternatively, a film 53 of amorphous siliconcontaining B or polycrystalline silicon containing B may first beformed, P or As may then be introduced into that part of the film 53which is the gate of the n-channel transistor, such that this part hasan P or As concentration higher than the B concentration.

In the case where an impurity is ion-implanted into the polycrystallinesilicon film 53, ions B⁺ are implanted into the film 53 at 1 to 20 keV,ions P⁺ are implanted at 5 to 30 keV, or the ions As⁺ are implanted at10 to 50 kev, at a dose which ranges from 5×10¹⁴ cm⁻² to 5×10¹⁵ cm⁻² inaccordance with the thickness of the polycrystalline silicon film 53.Thereafter, the polycrystalline silicon film 53 is heated, therebyelectrically activating the impurity.

In order to change the work function of the polycrystalline silicon(particularly, B-doped silicon), germanium (Ge) is ion-implanted in tothe film 53 at 10 to 40 kev at a dose of 1×10¹⁵ to 5×10¹⁶ cm⁻², therebyto form a Ge-containing film of polycrystalline silicon. Alternatively,the polycrystalline silicon film may be replaced by a germanium film.Furthermore, the polycrystalline silicon film may be replaced by asingle-crystal silicon substrate or an SOI single-crystal layer, whichexhibits thermal stability as high as that of the polycrystallinesilicon film. To reduce the contact resistance with electrodes,germanium may be ion-implanted into the a single-crystal siliconsubstrate or an SOI single-crystal layer (for example, into the sourceand drain regions, particularly into the source region), at a dose of1×10¹⁵ to 5×10¹⁶ cm⁻². In this case, too, the advantage resulting fromthe use of barrier metal is attained.

Sixth Embodiment

FIG. 9 is a sectional view depicting a MOSFET which is a sixthembodiment of the present invention. With reference to FIG. 9, themethod of manufacturing the MOSFET will be explained.

First, an insulating film 62, used as an element-isolating film, isformed in the surface of a silicon substrate 70, demarcating the surfaceregion of the substrate 70 into element-forming regions. Then, an n-typewell layer 71 and an n-type well layer 72 are formed two element-formingregions of the substrate 70, respectively. An n-type MOS transistor willbe formed in the p-type well layer 71, and a p-type MOS transistor willbe formed in the n-type well layer 72.

Next, a gate oxide film 63p is formed on the p-type well layer 71,and agate oxide film 63p on the n-type well layer 72. A polycrystallinesilicon film 64n containing an n-type impurity is formed on the gateoxide film 63n. A polycrystalline silicon film 64p containing a p-typeimpurity is formed on the gate oxide film 63p.

Further, reaction-preventing films 65n and 65p, each formed of nitrogen,tungsten and silicon, are formed on the polycrystalline silicon films64n and 64p, respectively. Two tungsten films 66n and 66p are thenformed on the reaction-preventing films 65n and 65p, respectively.Further, two silicon nitride (SiN) films 67n and 67p are formed on thetungsten films 66n and 66p, respectively. The silicon nitride films 67nand 67p each serve as a cap-insulating film.

Both reaction-preventing films 65n and 65p are formed in the same way asin the method of forming the gate electrode which is the fifthembodiment. Even if oxide films are naturally formed on thepolycrystalline silicon films 64n and 64p during the process of formingthe films 65n and 65p, the barrier at the interface between the film 64nand tungsten film 66n remains intact, and so does the barrier at theinterface between the film 64p and the tungsten film 66p.

Then, the polycrystalline silicon film 64n, the reaction-preventing film65n, the tungsten film 66n and the silicon nitride film 67n are etched,forming the gate electrode of the n-type MOS transistor. At the sametime, the polycrystalline silicon film 64p, the reaction-preventing film65p, the tungsten film 66p and the silicon nitride film 67p are etched,forming the gate electrode of the p-type MOS transistor.

Thereafter, the silicon contained in the polycrystalline silicon films64n and 64p, p-type well layer 71 and n-type well layers 72 are oxidizedby using N₂ gas and a mixture of H₂ gas and H₂ O gas. This oxidation iseffected by the method disclosed in Jpn. Pat. Appln. KOKAI PublicationNo. 60-9166. The oxide film on either gate electrode becomes thick atboth end portions of the gate electrode. Hence, either gate electrodeworks reliably even if electric fields are concentratedly applied to theends of the gate electrode.

In the present embodiment, the reaction-preventing films 65n and 65p aremade of the nitride of the same metal used as a component of the gateelectrodes. The films 65n an 65p are therefore reliably prevented frombeing oxidized excessively when the silicon they contain is oxidized.This is a new fact the inventors have come across. The reason why anexcessive etching of the films 65n and 65p is prevented has yet to bestudied. Needless to say, the films 65n and 65p may be made of thenitride of a metal different from the metal used as a component of thegate electrodes.

The above-mentioned metal is preferably such one as will reduce metalnitride in any subsequent heat treatment conducted in a reducingatmosphere. In the present embodiment, the metal is tungsten, and themetal nitride is tungsten nitride.

Tungsten nitride can be amorphous, depending on its nitrogen content. Inthe present embodiment, the reaction-preventing films 65n and 65pcontain 5 to 20% of nitrogen and are amorphous. The film 65n efficientlyprevents reaction between the polycrystalline silicon film 64n and thetungsten film 66n. The film 65p reliably prevents reaction between thepolycrystalline silicon film 64p and the tungsten film 66p. Since thereaction-preventing films 65n and 65p are amorphous, the grains of thetungsten films 65n and 65p formed on the films 65n and 65p,respectively, are large. Therefore, both tungsten films 65n and 65p havea low specific resistance.

After the silicon in the polycrystalline silicon films 64n and 65p,p-type well layer 71 and n-type well layer 72 has been oxidized asindicated above, impurities are ion-implanted into the layer 71, formingshallow, low impurity-concentration source and drains regions 68n, andinto the layer 72, forming shallow, low impurity-concentration sourceand drain regions 68p. Then, silicon nitride films 69n and 69p areformed. The film 69n covers the sides of the first gate electrode, andthe silicon nitride film 69n covers the top of the first gate electrode;the film 69p covers the sides of the second gate electrode, and thesilicon nitride film 69p covers the top of the second gate electrode.The tungsten films 66n and 66p have their sides covered by the siliconnitride films 69n and 69p, respectively, and will not be oxidized in anysubsequent process step.

Finally, impurities are ion-implanted into the p-type well layer 71,thereby forming source and drain regions 60n in the well layer 71.Similarly, impurities are ion-implanted into the n-type well layer 72,thereby forming source and drain regions 60p in the well layer 72 andfrom metal silicides 61n, 61p on the regions 60n, 60p. The COMStransistor of the structure shown in FIG. 9 is thereby manufactured.

The inventors hereof have found that if a titanium nitride film is usedas a reaction-preventing film, the following two problems will arise.

First, the reaction-preventing film is oxidized excessively sincetitanium nitride is very readily oxidized. This problem will bedescribed, with reference to FIGS. 14B and 14B. FIG. 14A is a sectionalview of a gate electrode formed on a silicon substrate 701. The gateelectrode is comprised of a gate oxide film 702 formed on the siliconsubstrate 701, a polycrystalline silicon film 703 formed on the film702, a titanium nitride film 704 formed on the film 703 and a tungstenfilm 705 formed on the film 704. When selective etching of silicon isperformed in order to increase the thickness of the end portions of theoxide film (not shown) formed on the gate electrode, the titaniumnitride film 704 is excessively oxidized at its sides, forming titaniumoxide (TiO₂) bumps 704a having a diameter of about 10 to 100 nm. Thesetitanium oxide bumps 704a make it difficult to form a homogeneousinsulating film (e.g., a silicon oxide film or a silicon nitride film)on the silicon substrate 701 by means of CVD method.

The second problem is that the titanium nitride grains formed on apolycrystalline silicon film are small. The tungsten film subsequentlyformed on the titanium nitride film formed of these small grainsinevitably has a high specific resistance.

In order to solve these problems, each reaction-preventing film of thepresent embodiment is made of the nitride of the same metal used as acomponent of the gate electrode, as is described above.

Seventh Embodiment

A gate electrode which is the seventh embodiment of the presentinvention will be described. It will be explained how to form this gateelectrode, with reference to FIGS. 10A to 10D.

First, as shown in FIG. 10A, a silicon oxide film 82, used as a gateoxide film, is formed on a silicon substrate 81. A polycrystallinesilicon film 83 having a thickness of 100 nm and containing a conductiveimpurity is formed on the silicon oxide film 82.

Then, as illustrated in FIG. 10B, a molybdenum nitride film 84 having athickness of 1 to 10 nm is formed on the polycrystalline silicon film83, and a molybdenum film 85 having a thickness of 10 nm is formed onthe molybdenum film 85. More precisely, reactive sputtering isconducted, using a molybdenum target, thus forming the molybdenumnitride film 84 on the polycrystalline silicon film 83. N₂ gas isexpelled from the process chamber used, and sputtering is then performedin the chamber now filled with Ar only. The molybdenum film 85 isthereby formed, without exposing the substrate 81 to the atmosphere.

Next, as shown in FIG. 10C, the resultant structure is subjected to heattreatment for 30 minutes at 800° C. or more in a reducing atmospherecontaining hydrogen. The molybdenum nitride film 84 is thereby changedinto a reaction-preventing film 56 which consists of molybdenum, siliconand nitrogen and which has a thickness of 1 nm or less. Since the heattreatment is carried out in a reducing atmosphere, the molybdenum film85 remains free of oxidation.

The reaction-preventing film 86 can easily be formed as designed, as isachieved in the fifth embodiment. Being electrically conductive, thefilm 86 has but a low contact resistance with the polycrystallinesilicon film 83, and also with the molybdenum film 85.

At last, as shown in FIG. 10D, the three-layer film formed of thepolycrystalline silicon film 83, the reaction-preventing film 86 and themolybdenum film 85 is patterned into a gate electrode.

In the embodiment described above, including the seventh embodiment, themulti-layer film is patterned after the reaction-preventing film hasbeen formed. Instead, the reaction-preventing film may be formed afterthe multi-layer film has been patterned.

The present invention has been made to solve a problem caused by asilicon nitride film interposed between a polycrystalline silicon filmand a refractory metal film. Namely, due to the silicon nitride film(i.e., a reaction-preventing film), the contact resistance between thepolycrystalline silicon film and the metal film increases to lengthenthe delay time of the semiconductor element which incorporates thepolycrystalline silicon film and the refractory metal film. This problemwill be described in detail, with reference to FIGS. 11A and 11B.

FIG. 11A is a sectional view of a gate electrode. The gate electrodecomprises a gate oxide film 92 formed on a silicon substrate 91, apolycrystalline silicon film 93, a silicon nitride film 94 formed on thefilm 93, and a tungsten film 95. The delay of signal transfer throughthe gate electrode of a semiconductor element is determined by twofactors. The factors are a gate capacitor C_(OX) and a contact resistorR_(C), both connected in series between the silicon substrate 91 and thetungsten film 95. FIG. 11B is an equivalent circuit diagram of thestructure shown in FIG. 11A. Here, the sheet resistance of the gateelectrode can be neglected to estimate the R_(C) caused R_(C) andC_(OX), because it contributes to the RC delay of the gate electrode,but far less than does the contact resistor R_(C).

As can be understood from FIGS. 11A and 11B, the contact resistor R_(C)and the gate capacitor C_(OX) cause the RC delay. The time constant ofthe RC delay is the product of the gate capacitor C_(OX) and the contactresistor R_(C). The resistor R_(C) is inversely proportional to the areaof the gate electrode, whereas the gate capacitor C_(OX) is proportionalthereto. Hence, the product of the resistor R_(C) and the gate capacitorC_(OX), i.e., R_(C) ×C_(OX), does not depend on the shape of the gateelectrode.

If the gate oxide film 92 is 7 nm thick, the gate capacitor C_(OX) willbe 4.9×10⁻¹⁵ F/μm². If the contact resistor RC is about 1×10³ Ωμm², thetime constant of the RC delay will be about 4.9×10⁻¹² sec, which isapproximately 5 psec. This RC delay is, as a matter of fact, one RCdelay component calculated based on the two factors only, i.e., thecontact resistor R_(C) and the gate capacitor C_(OX). There is anotherRC delay component which is determined by the sheet resistance of thegate electrode and the gate capacitor C_(OX).

The RC-delay component determined by the sheet resistance and the gatecapacitor C_(OX) will be explained, with reference to FIGS. 12A and 12B.As shown in FIG. 12A, the gate electrode has a contact resistor R_(C), agate capacitor C_(OX), a resistor R_(poly) of the polycrystallinesilicon film 93, and a resistor R_(W) of the tungsten film 95. FIG. 12Bis an equivalent circuit diagram of the structure shown in FIG. 12A. Asseen from FIG. 12B, the gate electrode is equivalent to a lumped R_(C)networks having five stages. The gate capacitor C_(OX) is invariable. Itis assumed here that the gate electrode is used in a semiconductorelement which has a channel length of 0.25 μm and a channel width of 20μm. The size of the element is similar to that of each MOSFET built in alogic LSI. Here, the delay time of the gate electrode is defined as thetime which elapses from the time when a input voltage pulse V_(in) (1V)rising fast within 0.01 psec is applied one end of the gate electrode,until the output voltage V_(out) at the other end (the polycrystallinesilicon film 93) of the gate electrode increases to 90% of the inputvoltage V_(in).

The inventors analyzed the relationship between the contact resistorR_(C) and the delay time. They found that the delay time sharplyincreased when the contact resistance R_(C) increased above 100 Ωμm², asshown in FIG. 13. They also found that the delay time reached 14 psecwhen the contact resistance R_(C) was 1 KΩμm².

In the case of an inverter comprising MOSFETs as small as the MOSFETexemplified above, the switching time of each inverter stage isestimated at 30 psec or less, neglecting the parasitic resistance andcapacitance of the MOSFET. With respect to this relatively shortswitching time, the RC delay time of 14 psec, described above, fallsoutside an allowable range.

In the case of a logic gate comprising the next-generation,sub-half-micron MOSFETs, the switching time of each stage is about a few10 psec. Hence, the longest RC delay time allowable for asub-half-micron MOSFET should be only a few picoseconds or less.

Eighth Embodiment

A MOSFET which is the eighth embodiment of this invention will now bedescribed, with reference to FIG. 15H which is a cross sectional view ofthe MOSFET.

As shown in FIG. 15H, the gate electrode of the MOSFET comprises apolycrystalline silicon film 112a, a silicon carbide film 115a formed onthe film 112a, a tungsten film 113a formed on the film 115a, and asilicon nitride film 117a formed on the film 113a. The gate electrode ischaracterized by the silicon carbide film 115a which is interposedbetween the polycrystalline silicon film 112a and the tungsten film 113aand which functions as a reaction-preventing film.

The silicon carbide film 115a prevents the polycrystalline silicon film112a and the tungsten film 113a from reacting with each other. Theresistance of the gate electrode is thereby decreased. Further, the film115a is resistant to the etching gas which is used for etching thetungsten film 113a and, therefore, prevents the polycrystalline siliconfilm 112a from being etched when the tungsten film 113a is etched withthe etching gas. In other words, the silicon carbide film 115a helps toachieve selective etching of the tungsten film 113a. Since the etchingof the film 115a little affects the polycrystalline silicon film 112a,the gate electrode can have a good shape and little critical dimensionlosses.

Having only a low resistance but also a shape as desired, the gateelectrode has but a very short RC delay and serves to miniaturize theMOSFET and raise the operating speed of the MOSFET.

A method of manufacturing the MOSFET shown in FIG. 15H will beexplained, with reference to FIGS. 15A to 15H which are sectional viewsexplaining the various steps of the method.

At first, as shown in FIG. 15A, a thin silicon oxide film 111, or a gateinsulating film, is formed on a silicon substrate 110. A polycrystallinesilicon film 111, about 100 nm thick, is then deposited on the siliconoxide film 111. A dopant, or an electrically active impurity, is addedto the polycrystalline silicon film 112 by means of, for example,vapor-phase diffusion.

Next, as shown in FIG. 15B, the silicon substrate 110 is heated to about800° C. in an atmosphere including a hydrogen carbide-based gas such asC₃ H₈. A silicon carbide film 115 having a thickness of about 10 nm isthereby formed on the polycrystalline silicon film 112.

Further, as illustrated in FIG. 15C, a tungsten film 113, about 100 nmthick, is formed by sputtering on the silicon carbide film 115. After900° C. annealing manufacturing the MOSFET, the resistance of the gateelectrode was measured. No increase in the resistance was observed.Rather, the resistance was found to have decreased. This means that thesilicon carbide film 115 prevented the polycrystalline silicon film 112and the tungsten film 113 from reacting with each other while thesilicon substrate 110 was being heated.

Thereafter, as shown in FIG. 15D, a silicon nitride film 117 having athickness of about 150 nm is formed on the tungsten film 113 by meansof, for example, CVD method. A photoresist, about 1 μm thick, isspin-coated on the silicon nitride film 117 thus formed. The photoresistis exposed to light through a photomask (not shown) and then developed,thereby forming a resist pattern 118 having a specific configuration.

Next, the silicon nitride film 117, the tungsten film 113 and thepolycrystalline silicon film 112 are etched by using the resist pattern118 as a mask, in a dry etching apparatus of the type illustrated inFIG. 17. The dry etching apparatus comprises an etching chamber 300, apre-etching chamber 400 and a post-etching chamber 500. A substrate 301is first introduced into the pre-etching chamber 400 and placed on atable 403 provided within the chamber 400. Then, the substrate 301 istransferred into the etching chamber 300 and placed on the electrode 302located within the chamber 300. After dry-etched, the substrate 301 istransferred from the etching chamber 300 into the post-etching chamber500 and mounted on a table 503 provided within the chamber 500.

The etching chamber 300 is connected to the pre-etching chamber 400 by agate valve 401, and to the post-etching chamber 500 by a gate valve 501.Substrates 301 can therefore be dry-etched, one by one, each within ashort time. Furthermore, the pre-etching chamber 400 and thepost-etching chamber 500 are sealed from the atmosphere by gate valves402 and 502, respectively, so that substrate 301 may not be adverselyinfluenced by the atmosphere.

The electrode 302 located within the etching chamber 300 is connected toa cooling pipe 303, so that its temperature is controlled to apredetermined value by the coolant circulated in the the cooling pipe303. Further, the electrode 302 is connected to a high-frequency powersupply 306 by a blocking capacitor 304 and a matching device 305. Thepower supply 306 supplies power of 13.56 MHz to the electrode 302. Whensupplied with this high-frequency power, the electrode 302 generatesplasma in the etching chamber 300.

Connected to the top of the etching chamber 300 is a reaction-gas supplyline 600. It is through this line 600 that a reaction gas is introducedinto the etching chamber 300. The reaction gas (i.e., etching gas) usedis, for example, a mixture of CHF₃ gas and CF₄ gas. The rate at whichthe gas is supplied into the chamber 300 is controlled to a desiredvalue by a valve 601 and a flow rate controller 602. The pressure in theetching chamber 300 is thereby maintained at a prescribed value.

Arranged right above the etching chamber 300 is a permanent magnet 307of about 200 gauss, which is connected to an electric motor 307 by ashaft 308 and can be rotated thereby. When the magnet 307 is thusrotated, a high ion-density plasma can be generated and maintained inthe etching chamber 300 even if a high vacuum on the order of 10⁻³ Torr.Many ions are emitted from the high ion-density plasma and applied ontothe substrate 301 mounted on the electrode 302. Dry etching is thusperformed on the substrate 301.

Using the resist pattern 118 as an etching mask, the silicon nitridefilm 117 is dry-etched by means of the dry etching apparatus, asillustrated in FIG. 15E. As a result of this, a silicon nitride film117a is formed which has desired size and shape. Thereafter, oxygenplasma is applied, removing the resist pattern 118.

Next, as shown in FIG. 15F, the tungsten film 113 is subjected toanisotropic etching, wherein the silicon nitride film 117a is used asthe etching mask and a mixture of SF₆ gas and Cl₂ gas is used as theetching gas. A tungsten film 113a of desired size and shape is therebyformed. The anisotropic etching is performed at a high-frequency powerof 0.7 W/cm², a pressure of 10 mTorr, by supplying SF₆ and Cl₂ gas atflow rates of 40 SCCM and 10 SCCM, respectively, while maintaining thetemperature of the electrode 302 at 70° C.

Under these etching conditions, the tungsten film 113 is etched at therate of about 180 nm/min, while the silicon nitride film 117 at the rateof about 50 nm/min. The ratio of etching rate of the tungsten film 113to that of the silicon nitride film 117 is about 3. Under the sameetching conditions, the silicon carbide film 115 is etched at the rateof about 35 nm/min. The ratio of etching rate of the tungsten film 113to that of the silicon carbide film 115 is therefore about 5. Therefore,if the tungsten film 113 is over-etched for the time required to etchaway 30% of the thickness (100 nm) of the tungsten film 113, the siliconcarbide film 115 located beneath the tungsten film 113 will be partlyetched to have its thickness reduced by about 6 nm. There is nopossibility that the silicon carbide film 115 is etched too much in theprocess of etching the tungsten film 113.

Thereafter, as shown in FIG. 15G, the silicon carbide film 115 issubjected to dry etching, wherein the silicon nitride film 117a is usedas the etching mask and a mixture of CF₆ gas, H₂ gas and O₂ gas is usedas the etching gas. A silicon carbide film 115a of desired size andshape is thereby formed. The dry etching is performed at ahigh-frequency power of 0.7 W/cm², a pressure of 10 mTorr, by supplyingC₂ F₆, H₂ gas and O₂ gas at flow rates of 40 SCCM, 10 SCCM and 1 SCCM,respectively.

Under these etching conditions, the silicon carbide film 115 is etchedat the rate of about 180 nm/min, while the silicon nitride film 117 atthe rate of about 100 nm/min. Hence, the ratio of etching rate of thesilicon carbide film 115 to that of the silicon nitride film 117 isabout 2. The ratio of etching rate of the silicon carbide film 115 tothat of the polycrystalline silicon film 112 is about 2. Therefore,over-etching of the silicon carbide film 115 will not influence thepolycrystalline silicon film 112 so much.

Then, as illustrated in FIG. 15H, the polycrystalline silicon film 112is subjected to anisotropic etching, wherein the silicon nitride film117a, the tungsten film 113a and the silicon carbide film 115a are usedas the etching mask and a mixture of HBr gas and O₂ is used as theetching gas. A polycrystalline silicon film 112a having desired size andshape is thereby formed. The film 112a, the tungsten film 113a, thesilicon carbide film 115a and the silicon nitride film 117a constitute agate electrode.

Finally, source and drain regions 121 are formed in the surface of thesilicon substrate 110 by means of ion implantation, heat treatment orthe like. Further, an inter-layer insulating film 119 and source anddrain electrodes 120 are formed by the method known in the art. As aresult, the MOSFET of the structure shown in FIG. 15H is manufactured.

As described above, the silicon carbide film 115 is provided between thepolycrystalline silicon film 112 and the tungsten film 113. It is thanksto the silicon carbide film 115 that the tungsten film 113 can besubjected to anisotropic etching in the present embodiment. The siliconcarbide film 115 will be described below in detail.

A silicon carbide film is comprised of two phases. The first phase has acomposition (Si:C=1:1) which is stoichiometrically stable. The secondphase is a SiC phase containing an excessive number of Si atoms or Catoms. Basically, a film of silicon carbide, which contains an excessivenumber of C atoms, is preferred as a reaction-preventing film for tworeasons. First, C atoms hardly react with refractory metal such astungsten (W), unlike Si atoms, since the diffusion constant of C atomsis far smaller than that of Si atoms in a metal film. Second, a siliconcarbide film has a higher density than a silicon carbide film containingan excessive number of Si atoms, and therefore helps Si atoms (capableof readily reacting with refractory metal) to diffuse into a film ofrefractory metal.

However, a silicon carbide film in which the ratio of C atoms exceeds 75atomic % becomes less resistant to oxidation when heated. It istherefore desired that a silicon carbide film whose carbon atom ratioranges from 50 to 75% be utilized in this invention. The most preferablefor use in the invention is a silicon carbide film which has a carbonatom ratio of about 50 atomic %.

Although silicon carbide is a semiconductor, it can have its specificresistance sufficiently reduced by adding to it an electrically activeimpurity. In the present invention, the silicon carbide film is formedby conducting heat treatment in a C₃ H₈ atmosphere. Thus, the siliconcarbide film can have a low sheet resistance of about 100 to about 1000Ω per unit area, merely by adding PH₃ gas to C₃ H₈. This specific sheetresistance is nearly equal to that of polycrystalline silicon.Phosphorus (i.e., an n-type impurity) in the PH₃ gas functions as anelectrically active impurity. There are some other electrically activeimpurities. Among them are n-type ones such as N, As and Sb and p-typeones such as B, Al and Ga.

The method of forming the silicon carbide film 115 is not limited to theone described above. Rather, the film 115 may be formed by two othermethods. The first alternative method is to electrically discharge acarbon-containing gas, generating plasma, and then apply the plasma ontothe surface of the polycrystalline silicon film 112. The secondalternative method is to apply a mixture of carbon gas and silicon gasonto the surface of the polycrystalline silicon film 112.

Ninth Embodiment

A MOSFET which is the ninth embodiment of the present invention will nowbe described. This MOSFET has the same structure as the MOSFET shown inFIG. 15H, which is the eighth embodiment of the invention.

A method of manufacturing this MOSFET will be explained, with referenceto FIGS. 16A to 16E and FIGS. 15D to 15H, which are sectional viewsexplaining the various steps of the method.

First, as illustrated in FIG. 16A, a silicon oxide film 221 is formed ona single-crystal silicon substrate 220. The silicon oxide film 221 has athickness of about 7 nm and is used as a gate oxide film. Apolycrystalline silicon film 222, about 100 nm thick, is deposited onthe silicon oxide film 221 by means of CVD method. A dopant, or anelectrically active impurity, is added to the polycrystalline siliconfilm 222 by means of vapor-phase diffusion.

Next, as shown in FIG. 16B, a carbide film 226 having a thickness ofabout 100 nm is formed by sputtering on the polycrystalline silicon film222.

Then, as shown in FIG. 16C, silicon ions (Si⁺) are implanted into theresultant structure, from above the carbide film 226 at an accelerationvoltage of 50 kev and a dose of 5×10¹⁵ cm⁻³. The acceleration voltage isset at the specific value of 50 keV in order that the projected range ofthe ions implanted may exist in the vicinity of the interface betweenthe polycrystalline silicon film 222 and the carbide film 226.

As a result of the ion implantation, C atoms and Si atoms mix togetherat the interface between the polycrystalline silicon film 222 and thecarbide film 226, forming a silicon carbide film 225. The siliconcarbide film 225 is about 10 nm thick and has a C atom ratio of about 60atomic %. The silicon carbide film 225 can be formed by another methodsuch as sputtering, as will be explained later.

The thickness of the silicon carbide film 225 depends on the dose ofsilicon ions implanted. If the dose is less than 5×10¹⁵ cm⁻³, thesilicon carbide film 225 will have a thickness of 5 nm or less and a Catom ratio of more than 75 atomic %. A silicon carbide film formed at anion dose of less than 5×10¹⁵ cm⁻³ cannot be used as areaction-preventing film. In view of this, it is necessary to implantsilicon ions at a dose of 5×10¹⁵ cm⁻³ or more. The preferable value forthe ion dose is reciprocally proportional to the mass number of the ionelement. In the case of ions of As (mass number: about 75), thepreferable ion dose is about 2×10¹⁵ cm⁻³ or more. If silicon ions areimplanted at a dose of 1×10¹⁷ cm⁻³ or more, the concentration of Siatoms will increase toward the bottom of the silicon carbide film 225.Nonetheless, the top region of the at portion of the film 225 on which arefractory metal film is to be formed later has a C atom ratio fallingwithin a range of 50 to 75 atom %, and the silicon nitride film 225 cantherefore effectively act as a reaction-preventing film.

Thereafter, as shown in FIG. 16D, the carbide film 226 is removed fromthe structure. At this time, the silicon carbide film 225 remains intactsince it is very resistant to oxidation.

Next, as illustrated in FIG. 16E, a tungsten film 223, about 100 nmthick, is formed by sputtering on the silicon carbide film 225.

A structure shown in FIG. 16E was actually heated at 800 to 900° C. Noincrease was found in the resistance of a gate electrode. This meansthat the silicon carbide film 225 formed through the mixture of C atomsand Si atoms induced by the ion implantation did effectively worked as areaction-preventing film.

Since ions of an electrically active impurity are implanted to form thesilicon carbide film 225, the formation of the silicon carbide film 225and the doping of the polycrystalline silicon film 222 can beaccomplished in a single process step, i.e., the implantation of thoseimpurity ions. Furthermore, the polycrystalline silicon film 222 canhave a desired resistance, merely by selecting the conductivity type ofthe impurity ions. Still further, the structure shown in FIG. 16C may beheated after the ion implantation, thereby to impart a higher density tothe silicon carbide film 225 and ultimately enable the film 225 tofunction as a more effective reaction-preventing film.

Thereafter, the films 221, 222, 225 and 223 are etched in the sameapparatus, at such etching rates and by using the same etching gases asin the eighth embodiment and as explained with reference to FIGS. 15D to15G. Finally, source and drain regions are formed in the surface of thesilicon substrate 220, an inter-layer insulating film and source anddrain electrodes are formed in the same manner as in the eighthembodiment and as described with reference to FIG. 15H. As a result, theMOSFET of the structure shown in FIG. 15H is manufactured.

In the ninth embodiment, the silicon carbide film 225 is formed by ionimplantation. Instead, a silicon carbide film may be formed bysputtering. In this sputtering method, a compound target made of SiChaving a stoichiometrically stable composition (Si:C=1:1) is spacedapart from the substrate 220 by a distance of 10 cm, and is RF-sputteredat an Ar gas pressure of 10 mTorr, thereby forming a silicon carbidefilm. The silicon nitride film, thus formed, has a composition of:Si:C=4:6. In other words, this film is made of carbon-rich siliconcarbide. This is because C atoms have a longer mean free path than Siatoms. The longer the distance between the substrate and the target, themore carbon-rich the silicon carbide is. It follows that the siliconcarbide film can have a C atom ratio of 50 to 70 atomic %, only byadjusting the distance between the substrate and the target.

Alternatively, a silicon carbide film may be formed by performingreactive sputtering on a silicon target, by using, as the sputteringgas, a mixture of a carbon-containing gas such as CH₄ gas and an inertgas such as Ar gas. In this sputtering method, a sputtering gas and atarget may be used as sputtering the silicon source and the carbonsource, respectively. More specifically, a carbon target may besubjected to reactive sputtering, using a mixture of asilicon-containing gas such as SiH₄ and an inert gas such as Ar gas, toform a silicon carbide film; or a SiC target may be subjected toreactive sputtering, using a mixture of a carbon-containing gas such asCH₄ or a silicon-containing gas such as SiH₄ and an inert gas such as Argas, to form a silicon carbide film.

In the eighth and ninth embodiments, the silicon carbide film isinterposed between the tungsten film and the polycrystalline siliconfilm. The tungsten film may be replaced by any other metal film that isetched at a lower rate than the silicon film provided underneath andthat can react with silicon when heated at 600° C. or more to form metalsilicide. Furthermore, the polycrystalline silicon film may be replacedby a film of single-crystal silicon, amorphous silicon film or the like,which is more heat-resistant and less readily etched than refractorymetals. If the tungsten film may be replaced by such an other metalfilm, or if the polycrystalline silicon film is replaced by a film ofother silicon material, the advantages of the eighth and ninthembodiment will be attained, as well.

Both the eighth embodiment and the ninth embodiment are each a gateelectrode of a MOSFET. Nevertheless, the present invention can beapplied to the electrodes of any other type of a transistor, such as abipolar transistor. Moreover, this invention can be applied toelectrodes and wiring which have a low resistance, which are shaped asdesigned, which are thin and small, and which are, therefore, suitablefor use in, particularly, semiconductor memory devices and semiconductorintegrated circuits.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details, representative devices, andillustrated examples shown and described herein. Accordingly, variousmodifications may be made without departing from the spirit or scope ofthe general inventive concept as defined by the appended claims andtheir equivalents.

What is claimed is:
 1. A method of manufacturing a semiconductor device,comprising the steps of:forming a semiconductor film consistingessentially of a semiconductor containing a semiconductor element on asubstrate; depositing a first conductive film containing a metal andnitrogen on said semiconductor film, said metal being of such a typethat a decrease in Gibbs free energy occurring in forming a nitride ofsaid metal from said metal is smaller than a decrease in Gibbs freeenergy occurring in forming a nitride of said semiconductor element fromsaid semiconductor element; and heating said first conductive film,thereby changing all or part of said first conductive film to a secondconductive film consisting essentially of said metal, and therebyforming a third conductive film containing nitrogen and saidsemiconductor element and positioned in contact with said semiconductorfilm between said second conductive film and said semiconductor film toform at least one of an electrode and a wiring which includes saidsemiconductor film, said second conductive film, and said thirdconductive film.
 2. The method according claim 1, further comprising astep of depositing a metal film consisting essentially of a metal onsaid first conductive film, between said step of depositing said firstconductive film and said step of heating said first conductive film. 3.The method according to claim 2, wherein said first conductive film andsaid metal film consist of the same metal.
 4. The method according toclaim 1, wherein said semiconductor element consists of silicon, andsaid metal of said first conductive film consists of a metal selectedfrom the group consisting of tungsten, molybdenum, niobium, tantalum,and copper.
 5. The method according to claim 4, wherein saidsemiconductor consists essentially of silicon.
 6. The method accordingto claim 1, wherein said at least one of an electrode and a wiringcomprises a gate electrode.
 7. A method of manufacturing a semiconductordevice, comprising the steps of:forming a semiconductor film consistingessentially of a semiconductor containing a semiconductor element on asubstrate; depositing a first conductive film containing a metal andnitrogen on said semiconductor film, said metal being of such a typethat a decrease in Gibbs free energy occurring in forming a nitride ofsaid metal from said metal is smaller than a decrease in Gibbs freeenergy occurring in forming a nitride of said semiconductor element fromsaid semiconductor element; and heating said first conductive film,thereby changing all or part of said first conductive film to a secondconductive film containing nitrogen, said metal, and said semiconductorelement, and positioned in contact with said semiconductor film to format least one of an electrode and a wiring which includes saidsemiconductor film and second conductive film.
 8. The method accordingto claim 7, further comprising a step of depositing a metal filmconsisting essentially of a metal on said first conductive film, betweensaid step of depositing said first conductive film and said step ofheating said first conductive film.
 9. The method according to claim 8,wherein said first conductive film and said metal film consist of thesame metal.
 10. The method according to claim 7, wherein saidsemiconductor element consists of silicon, and said metal of said firstconductive film consists of a metal selected from the group consistingof tungsten, molybdenum, niobium, tantalum, and copper.
 11. The methodaccording to claim 10, wherein said semiconductor consists essentiallyof silicon.
 12. The method according to claim 7, wherein said at leastone of an electrode and a wiring comprises a gate electrode.
 13. Themethod according to claim 1 or 7, wherein said semiconductor film is asilicon film or a silicon germanium film.
 14. A method of manufacturinga semiconductor device, comprising the steps of:forming a silicon filmon a semiconductor substrate; forming a silicon carbide film on saidsilicon film, said silicon carbide film having a ratio of carbon atomsranging from 50 to 75 atomic %; forming a metal film on said siliconcarbide film; and performing selective anisotropic etching on saidsilicon film, said silicon carbide film and said metal film to form atleast one of an electrode and a wiring.
 15. The method according toclaim 14, wherein said step of forming said silicon carbide filmcomprises the steps of:forming a carbon film on said silicon film; andimplanting ions into said carbon film to mix carbon atoms and siliconatoms at an interface between said carbon film and said silicon film.16. The method according to claim 15, wherein said ions are those of anelectrically active impurity.
 17. The method according to claim 14,further comprising a step of oxidizing a part of said silicon film. 18.A method of manufacturing a semiconductor device, comprising the stepsof:forming a semiconductor film consisting essentially of asemiconductor containing silicon on a substrate; depositing a firstconductive film containing tungsten and nitrogen on said semiconductorfilm; and heating said first conductive film, thereby changing all orpart of said first conductive film to a second conductive filmconsisting essentially of tungsten, and thereby forming a thirdconductive film containing nitrogen and silicon and positioned incontact with said semiconductor film between said second conductive filmand said semiconductor film to form at least one of an electrode and awiring which includes said semiconductor film, said second conductivefilm, and said third conductive film.
 19. The method according to claim18, further comprising a step of depositing a metal film consistingessentially of tungsten on said first conductive film, between said stepof depositing said first conductive film and said step of heating saidfirst conductive film.
 20. Tho method according to claim 18, whereinsaid semiconductor consists essentially of silicon.
 21. The methodaccording to claim 18, wherein said at least one of an electrode and awiring comprises a gate electrode.
 22. A method of manufacturing asemiconductor device, comprising the steps of:forming a semiconductorfilm consisting essentially of a semiconductor containing silicon on asubstrate; depositing a first conductive film containing tungsten andnitrogen on said semiconductor film; and heating said first conductivefilm, thereby changing all or part of said first conductive film to asecond conductive film containing nitrogen, tungsten, and silicon, andpositioned in contact with said semiconductor film to form at least oneof an electrode and a wiring which includes said semiconductor film andsecond conductive film.
 23. The method according to claim 22, furthercomprising a step of depositing a metal film consisting essentially oftungsten on said first conductive film, between said step of depositingsaid first conductive film and said stop of heating said firstconductive film.
 24. The method according to claim 22, wherein saidsemiconductor consists essentially of silicon.
 25. The method accordingto claim 23, wherein said at least one of an electrode and a wiringcomprises a gate electrode.